1. Field of the Invention
The present invention relates to a content delivery network and, in particular, to determining round-trip time between a local domain name server and an edge point of presence in the content delivery network.
2. Description of the Related Art
A content delivery network (CDN) uses the round-trip time (RTT) between a local domain name server (LDNS) of a user and points of presence (POPs) within the CDN to direct user requests for content. Conventional methods for determining RTT time from a POP to a LDNS use one or more of ping, traceroute, reverse DNS lookup and opening a Transmission Control Protocol (TCP) connection. However, for many reasons, an LDNS may fail to respond to the conventionally used methods, preventing the CDN from obtaining RTT data. Further, some intermediate routers between an edge POP and a LDNS may fail to respond to conventional methods, preventing RTT data acquisition from the LDNS. For example, some routers may unconditionally drop traceroute requests, preventing data retrieval from the LDNS. Such inability of conventional methods to accurately calculate RTT between an edge POP and non-responsive LDNSes impairs CDN performance.